This routine shapes and tones all the muscles in the legs. Perform these exercises two or three times a week, and you should see a difference in four weeks.

Warm-up: SkippingSkip for three minutes. Repeat three times. Tip: If you don't have a jump rope, pretend to swing one.

Photograph: Jakob N. Layman

Front lunges(1) From standing, step your right leg forward into the low lunge position. The knee should not extend past the toe. (2) Step your leg back to the starting standing position. (3) Repeat with your left leg.Repeat ten times, perform three sets. To increase the difficulty, hold light dumbbells in each hand.

Photograph: Jakob N. Layman

Squats(1) Standing with your feet together, step your right leg to the right side and lower your butt, as if you're sitting down in a chair. (2) Dynamically push up with the right leg and step the right leg back to the starting position. (3) Repeat on the left side.Repeat ten times; perform three sets. To make it harder, lift your leg out laterally before stepping back in.

Photograph: Jakob N. Layman

Pistol squats(1) Standing with a chair behind you and your arms extended out to the front for balance, raise your right leg off the ground, bend your left leg at the knee and sit in the chair.(2) Push up with your left leg.Repeat ten times, switch legs and perform the movements ten more times; perform the combined sets three times.

Photograph: Jakob N. Layman

Single-leg floor bridges(1) Lying on your back with your arms extended by your side with palms facing up, bend your knees and bring your heels toward your butt. (2) Extend your right leg up toward the ceiling. Use your left leg to push your hips up, then lower them to the floor.Repeat the movements in (2) ten times, switch legs and do ten more; perform the combined sets three times.

Photograph: Jakob N. Layman

Straight-leg raises(1) Kneeling on an inclined bench or lying on your left side, raise your right leg up.(2) Move your raised leg until it is straight in front or you, return it to the center, move it until it is straight behind you and return to the center again.Repeat 12 times, switch sides and legs, and perform the movements 12 more times; perform combined sets three times.

Photograph: Jakob N. Layman

squatjumps2

Photograph: Jakob N. Layman

Butt blaster(1) Kneeling with your hands on the floor shoulder-width apart, raise your right leg straight up. (2) Move your right leg toward the left side of your body, crossing the left leg and set your toes down. Raise your leg back to center.(3) Move the same leg over to the right side of your body, set your toes down and return to the center.Repeat movements (2) and (3) ten times, switch legs and perform the exercise ten more times; perform three sets.

Photograph: Jakob N. Layman

Calf raises(1) Placing your hands on a wall for support, stand on your right leg and raise your body up on the ball of your foot.(2) Lower your heel toward the ground, but don't quite touch the floor. Repeat 30 times, switch legs and perform the exercise 30 more times; perform three sets. (3) Finish with a standing calf stretch against the wall.

Photograph: Jakob N. Layman

Mountain climbers(1) In the high push-up position, rapidly tuck your right knee in toward your chest, then back out(2) Repeat with the left leg. You should feel like you're running in place or climbing a mountain.Repeat movements for 30 seconds; perform three times.

Koschak's fitness favorites

"Ice-skating is the perfect way to keep moving during the holidays. I love the rink at Bryant Park, and if you pay the small VIP fee you can skip the line." Citi Pond at Bryant Park, Sixth Ave between 40th and 42nd Sts (212-661-6640, citipondatbryantpark.com). Free; skate rental $14. VIP fast pass $20, skate rental included.

"Everyone needs relaxation and rest. What better way to do this than at a spa? My favorite is Spa Castle in Queens. Yes, I know it's Queens, but it's worth the journey. I highly recommend the hot-stone massage." 131-10 Eleventh Ave at 131st St, College Point, Queens (718-939-6300, nyspacastle.com). Weekday entry $35, weekend entry $45. Hot-stone massage $160.

"I use the supplement Amino Boost XXL prior to working out. It contains all of the essential amino acids, including leucine, which helps to burn fat. It tastes like fruit punch, it's calorie free, and it contains no caffeine." dotfit.com/aminoboostxxl